The present invention relates to recovering the fuel value from waste sludges and in particular to recovering and reclaiming the fuel value from crude oil tank bottoms.
There are numerous sources which produce organic hydrocarbon containing waste sludges as by-products. Due to environmental regulations and lack of landfill space, there is an increased desire to treat sludge waste products in the most economically feasible manner. Treatment methods which are acceptable for either reclaiming or disposing of hydrocarbon sludges vary depending on the chemical makeup of the sludge. U.S. Pat. No. 5,154,831 details the various components which are present in sludges from various sources.
A particular problem arises with removal and treatment of the sludge which accumulates on the bottom of crude oil storage tanks. Heavy crude oil often can contain as much as 3 to 5% of the crude oil volume in globular form. When this crude oil is put into storage tanks, the globular oil settles to the bottom of the tank. As successive loads of crude oil are transitioned through the tank, a thick layer of the settled globular oil accumulates in the bottom of the tank. This settled globular oil is commonly referred to as crude oil tank bottoms or crude oil sludge.
Most refineries periodically take the storage tanks out of service, cut a hole in the side of the tank, and remove the bottoms. Alternately the bottoms of the storage tanks can be removed using one of several known techniques utilizing chemicals or cutter stock. The residual solids are usually disposed of in a landfill or incinerated.
For example, U.S. Pat. No. 4,014,780 to McCoy teaches a distillation technique for treating refinery sludge so it is suitable for disposal in a landfill. Biceroglu, U.S. Pat. No. 5,288,391, teaches a process involving separating a sludge into two phases by distillation. U.S. Pat. No. 4,931,161 to Sundar teaches a process for solidifying a waste sludge by adding a binder. U.S. Pat. No. 5,288,413 to Chu discloses a process whereby a solid fuel is formed from a sludge wherein the waste sludge is filtered and dried. Sims et al., U.S. Pat. No. 5,328,105 discloses a transportable processing unit for treating organic wastes.
In spite of the prior art attempts, up to this point, there has not been an effective process for treating crude oil tank bottom sludge which employs a single apparatus which both removes the crude oil sludge from the storage tank, and performs subsequent processing of the removed sludge so that the fuel value contained in the sludge may be recovered.